Field of the Invention
The invention relates to a circuit configuration for regulating a current fed to an electromechanical component of an automobile.
A circuit configuration of this type serves for regulating the current fed to the electromechanical component in the motor vehicle in particular a coil current for a hydraulic pressure regulating valve of an automatic motor vehicle transmission. It has a circuit carrier containing conductor tracks and components for controlling the electromechanical component, and also a current measuring resistor, whose signal is evaluated during the current regulation.
A device for detecting a load current is known from Published, Non-Prosecuted German Patent Application DE 42 23 338 A1, to be precise, a regulator with overload protection. A signal derived from a current measuring resistor and a reference signal are fed to an operational amplifier. The current measuring resistor is configured as a conductor track of a printed circuit. The reference signal is applied to a second input of the operational amplifier via a further conductor track. The two conductor tracks are constructed identically and are in good thermal contact. As a result, the load current is detected in a temperature-compensated fashion.
In the case of error compensation for measuring instruments, the measured values of the latter are calculated in a microcomputer as is known in German Patent DE 26 30 958 B2. The microcomputer is assigned memories in which are stored correction values, correction curves of reference quantities and of components, temperature coefficients, temperature profile curves and aging rates of the reference quantities and components. The correction values are measured using an analog-to-digital converter dedicated to the measuring instruments, and therefore contain this error as well. The measuring instruments register the time that has elapsed since a measuring instrument was used, and all of the stored correction values are taken into account in the calculation of the final measured values. The output signal of a temperature sensor and the stored temperature coefficients and curves are also taken into account in the calculation.
In the case of current regulators subjected to high temperature fluctuations, it is customary to bond a current measuring resistor made of constantan or a similar high-quality alloy on that side of the circuit carrier which bears the components, and to make contact with it by bonding wires. Although this enables accurate current measurement in a wide temperature range, such precision current measuring resistors are nonetheless expensive.